A stolen vehicle “chop shop” operated by undercover detectives for nearly a year in Lemon Grove led to the indictments of 42 people suspected of auto theft and gun and drug sales, authorities announced Thursday.

Thirty-two defendants have been arrested, most during an early-morning sweep Wednesday throughout San Diego County, Chief Deputy District Attorney Summer Stephan said at a news conference in downtown San Diego. The raids were aided by more than 200 law enforcement officers who used Qualcomm Stadium as a processing point for the large number of arrestees.

Ten defendants remain at-large.

The undercover investigation, led by the California Highway Patrol’s Regional Auto Theft Task Force and dubbed “Operation Kwik Boost,” began in January after authorities noticed an uptick in auto thefts in the East County, said CHP Capt. Don Goodbrand, task force commander.

The task force detectives set up an undercover storefront in Lemon Grove, where car thieves would bring by stolen vehicles and sell them to the detectives to be broken up into smaller parts.

Except the cars didn’t get chopped. The detectives held onto the stolen vehicles for about a week or so to keep up appearances, then returned them to their rightful owners.

Investigators were able to seize 117 stolen vehicles valued at $1.3 million.

“While some people see auto theft as a property crime only, dozens of these vehicles were stolen from families that did not have insurance to replace the vehicles,” Goodbrand said. “And these were their only vehicles, their sole method of transportation to get their kids to and from school, to work and run their daily errands.

“To be able to recover these vehicles and return them to their rightful owners was especially rewarding to myself and my staff,” he said.

Authorities said during the course of the operation, they identified about 10 different auto theft rings, most of which targeted vehicles in the East County and South Bay.

Even though there wasn’t one central hierarchy, many of the thieves knew each other, authorities said.

During the investigation, detectives also learned some of the thieves were selling firearms and drugs. In June, the task force asked the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives to join the investigation.

ATF agents focused on firearms deals, seizing 51 guns — from run-of-the-mill pistols and rifles to homemade AR-15-type assault rifles and a silencer, said John D’Angelo, ATF’s assistant special agent in charge in San Diego.

Peggy Peattie / San Diego Union-Tribune

Authorities indicted 42 people in San Diego County as part a nearly yearlong investigation into auto thefts. Those shown in this photo remain at-large.

Authorities indicted 42 people in San Diego County as part a nearly yearlong investigation into auto thefts. Those shown in this photo remain at-large. (Peggy Peattie / San Diego Union-Tribune)

Six defendants were arrested this week on federal gun-related charges and three search warrants served.

Investigators also seized 5½ pounds of methamphetamine, 3 kilograms of cocaine and 15 pounds of marijuana.

The large-scale nature of the case required a two-week presentation to a county grand jury to obtain the indictments on the state charges, the District Attorney’s Office said.

While investigators identified 92 suspects during the operation, indictments were secured against less than half. The investigation remains ongoing, authorities said.

The defendants who have been arrested and are facing state charges are set to be arraigned in San Diego Superior Court on Friday.

The number of vehicles stolen in San Diego County continues to hover around 10,000 a year, Stephan said. That is about 60 percent less than the number stolen in 2007.

Because of the Regional Auto Theft Task Force’s efforts, she said, “our county went from being No. 3 in the nation for auto theft to No. 15.”

Crime statistics for the first half of 2016 show auto thefts jumped 16 percent in San Diego County compared to the same period last year, according to the San Diego Association of Governments, which tracks crime trends.